a = c("A", "B")
b = c("X", "Y")

res1 <- list()

for (i in a) {
  set.seed(123)
  for (j in b) {
    res1[[paste0(i, j)]] <- rnorm(1)
  }
}

res2 <- list()

set.seed(123)
for (j in b) {
  res2[[paste0(i, j)]] <- rnorm(1)
}

res1
res2